In all reality, the anus isn’t visible on a nude person. And since when is the anus genitalia? I don’t think the article states anything about anus, rectum, or colon being exposed. The guys butt was showing which is probably contrary to a local ordinance. The end of the article implies the dudes testicles(balls, boys, nuts, etc) may have been exposed.
In reality the gluteous-maximi are what covers the “anus” unless someone desides to “bend over and spread-em”.